watchOS 5.3 (build 16U5545c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2019-06-11T17:13:38Z. The update package is 176.56 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8a2bb358da39db1c3d06014e97963e7ad3bdbb6e.zip.